This invention relates to an approximately 74,000 Dalton (74 kD) outer membrane protein purified from Moraxella catarrhalis. 
Moraxella (Branhamella) catarrhalis is one of the major bacterial pathogens causing otitis media in children (Bibliography entries 1,2,3,4). It also causes sinusitis, laryngitis, tracheitis, pneumonia, and other respiratory diseases in children and adults (5,6,7). A prophylactic vaccine is clearly needed because nearly all clinical isolates are resistant to xcex2-lactam antibiotics (8,9).
The outer membrane proteins (OMPs) of M. catarrhalis are being investigated as potential vaccine candidates because they are readily accessible to antibodies. Indeed, antibodies elicited in mice towards certain OMP""s including UspA and the CopB have already been shown to have biological activity, such as bactericidal activity, adhesion blocking activity and enhanced pulmonary clearance of the bacteria in an animal model (10,11,12,13). Serology data from humans who have suffered a recent M. catarrhalis infection indicates that humans develop antibodies towards OMP""s following natural infection (14,15,16,17,18). This suggests that OMP""s are the targets of the host""s defense mechanisms. UspA-specific antibodies are present in normal human serum and these antibodies have bactericidal activity. There are also high levels of antibodies towards OMPs of approximately 80 kD in sera from both healthy humans and patients recovering from recent M. catarrhalis infections (16). Several proteins from M. catarrhalis migrate within this size range. Among them are CopB (12), the B1 protein (18), a transferrin binding protein (TbpB) and a lactoferrin binding protein (LbpB) (19) Whether these proteins are the same or different from one another has yet to be determined. None of them, however, has been evaluated in a purified form for vaccine use.
An efficacious vaccine to protect against diseases caused by M. catarrhalis should confer protection at all stages of disease. These stages include bacterial colonization on mucosal surfaces, bacterial multiplication, spread and invasion, and the development of inflammatory response. Multiple bacterial components may be required to formulate an efficacious vaccine. Although there is pre-clinical data to suggest that some surface components of M. catarrhalis are potential vaccine antigens, it is as yet unclear if these components will confer sufficient protective immunity in humans. Thus, it is important to identify and evaluate new bacterial antigens for vaccine use.
Accordingly, it is an object of this invention to isolate, purify and characterize an additional protein from M. catarrhalis. It is a further object of this invention to test whether this protein is a viable vaccine candidate in appropriate model systems.
These and other objects of the invention as discussed below are achieved by the isolation and purification of a protein from M. catarrhalis which is designated the 74 kD protein, based on approximate molecular weight as measured by mass spectrometry, as well as peptides of the 74 kD protein comprising an epitope or epitopes thereof. The isolated and purified 74 kD protein from M. catarrhalis has an amino-terminal amino acid sequence which is conserved among various strains of M. catarrhalis. This amino-terminal amino acid sequence comprises the sequence Xaa Gly Gly Ser Gly Gly Ser Asn Pro Pro Ala Pro Thr (SEQ ID NO:1), where the first residue is not identified, or a biologically equivalent amino-terminal amino acid sequence thereof. The protein of this invention has a molecular weight of approximately 74.9 kD as measured on a 10% SDS-PAGE gel, while its molecular weight as measured by mass spectrometry is approximately 74 kD.
In another embodiment of this invention, the isolated and purified 74 kD protein or a peptide of the 74 kD protein comprising an epitope or epitopes thereof, is used to prepare a vaccine composition which elicits a protective immune response in a mammalian host. The vaccine composition may further comprise an adjuvant, diluent or carrier. Examples of such adjuvants include aluminum hydroxide, aluminum phosphate, MPL(trademark), Stimulon(trademark) QS-21, and IL-12. The vaccine composition is administered to a mammalian host in an immunogenic amount sufficient to protect the host against disease caused by M. catarrhalis. 